Alloimmunization to antigens on platelets is one of the most severe limiting factors in platelet transfusion. In this application to become a member of a cooperative trial for the prevention of alloimmunization, we propose two strategies which might limit alloimmunization from this source in patients treated for acute non-lymphocytic leukemia: 1. selection of platelet donors by matching HLA antigens, particularly the so-called "public" antigens; 2. removal of leukocytes from platelet products by filtration. In a cooperative study, we would be able to implement other strategies if they were selected. We also propose methods for following the development of alloimmunization to both HLA and platelet-specific antigens and for determining the epidemiology of alloimmunization.